This invention relates generally to fluid pumps and particularly to those capable of precision fluid flow and/or metering delivery.
Pumps comprise one of the most common and well developed as well as well known types of basic machines. The essential function of a pump is the displacement and movement or pressurization of a fluid. The majority of pumps may be divided into a basic classification as either reciprocating or rotary action pumps. Reciprocating pumps typically utilize one or more cylinders together with appropriate valves for controlling fluid flow to and from the cylinders. Each cylinder is fitted with a moving piston which in turn is usually coupled to crank mechanism for imparting piston movement within the cylinder in response to rotation of an input power or drive shaft.
One of the more recently developed types of reciprocating pumps is generally referred to as a xe2x80x9crod pumpxe2x80x9d. Rod pumps typically find use in high precision or fluid metering applications. Typically, rod pumps utilize a fluid cylinder having a closed end bore within which a pump rod is moved. The open end of the fluid cylinder bore supports a pressure seal against the pump rod for maintaining pressure within the cylinder bore. As the pump rod is drawn from the cylinder bore, low pressure or xe2x80x9cdrawxe2x80x9d is created in the cylinder bore allowing fluid flow into the cylinder. Conversely, as the pump rod is driven into the cylinder bore the fluid is pressurized. Combinations of check valves are typically used to control fluid flow to and from the pump.
In contrast, rotary pumps may be generally characterized as apparatus having a shaft coupled to a source of rotary power which is supported within a pump body. The latter, defines a chamber or cavity within which a fluid movement or displacement device is rotated by the input power shaft. Perhaps the most pervasive type of rotary pump may be generally described as an impeller type pump. In such pumps, a rotor is positioned within the pump chamber and rotated by the input power shaft. The rotor in turn supports a plurality of blades which are sized and configured in general correspondence with the interior chamber of the pump housing. An input port and an output port are formed in the pump housing in communication with the chamber. As the input drive shaft rotates the rotor and its plurality of impeller blades within the pump chamber, the fluid is drawn into the chamber through the input port and forced outwardly through the output port.
Another type of rotary pump is typically referred to as a turban or vane type pump. The turban or vane pump utilizes a housing defining a chamber which is usually cylindrical in shape which supports a plurality of static vanes radially disposed within the chamber interior. An armature is rotatably supported within the pump chamber and further supports a plurality of rotating vanes which are moveable with respect to the static vanes. A drive shaft is coupled to a source of operative rotary power and is further coupled to the armature. As rotary power is applied to the armature, the interaction of the rotating vanes and static vanes produces a turban-like displacement of the fluid within the chamber. Typically an input port is coupled to one end of the chamber while an output port is coupled to the downstream end of the pump chamber.
Still another type of rotary action pump is referred to generally as a xe2x80x9cperistalticxe2x80x9d which is often referred to as a xe2x80x9chose pumpxe2x80x9d. Peristaltic pumps utilize a housing within which a generally cylindrical chamber is formed. A flexible tubing or hose is positioned against the outer surface of the housing chamber. One end of the tubing or hose is coupled to an input fluid supply while the remaining end forms an output port for the pump. A rotor is rotatably supported within the chamber and further supports one or more rollers about its periphery. The rollers are positioned against the flexible tubing or hose and are of sufficient size to deform the hose to provide pinching or closure at the point of roller pressure. A drive shaft is coupled to the rotor and to a source of rotational power. As the rotor rotates, the rollers displace quantities of fluid in the direction of rotor rotation to transfer the fluid from the input source to the output port.
While most pumps are used in applications which require the pumps to simply run for relatively long periods at a so-called steady state, in certain environments pumps must also be capable of providing short term small volume runs to transfer fluid in more precise quantities. Such pumps are often referred to as xe2x80x9cfluid meteringxe2x80x9d pumps and are characterized by precise volume delivery of fluid. In many instances, such fluid metering pumps are used in an operative environment in which the rotating member is moved through small angular displacements substantially less than a full rotation.
While the above described prior art pumps have been the subject of substantial refinement and development, they have yet to provide pumps which are capable of both steady state operation and fluid metering operation. Many of the above described prior art pumps have been subject to an undesirable tendency to impart a pulsating characteristic to the fluid flow. There remains therefore a continuing need in the art for an improved pump which is capable of providing smooth pulse free fluid flow as well as accurate fluid metering operation.
Accordingly, it is a general object of the present invention to provide an improved precision flow pump. It is a more particular object of the present invention to provide an improved pump which is capable of providing extremely precise fluid metering operation through partial pump strokes as well as relatively pulse-free fluid flow during more conventional continuous pump action.
In accordance with the present invention there is provided a double-acting rod pump comprising: a frame support; a carriage slidably movable upon the frame support in first and opposed directions; at least one first rod pump section coupled to the carriage and the frame support; at least one second rod pump section coupled to carriage and the frame support in an operational relationship opposite to the at least one first rod pump section; a pump screw rotatably supported by the support frame; a bi-directional motor for rotating the pump screw in first and second rotational directions; engagement means on the carriage for engaging the pump screw such that first and second rotational direction rotation of the pump screw moves the carriage in opposed first and second direction movement; and valve means coupled to the at least on first rod pump section and the at least one second rod pump section for controlling fluid flow to and from the first and second rod pump sections.